Experiments already completed by the investigator indicate that the potassium control system is complex and involves dynamic interactions among several feedback control loops. The experiments in the first part of the proposal are designed to quantitatively analyze the operation of each of these loops and then to use this experimental information to construct a mathematical model of the system that will lead to an understanding of the interactions of the components. The end result will be a complete understanding of the control of potassium distribution, excretion, and extracellular concentration. The second part of the proposal is designed to quantitatively assess the long-term effects of changes in total body potassium and extracellular potassium concentration on the pumping ability of the heart, vascular control and renal function. This information is of immediate clinical importance in diseases involving these organ systems as well as in conditions in which potassium control is abnormal.